Vitamin B group compounds, such as folic acid and vitamin B.sub.2, are incorporated in various food, pharmaceutical, feed and other compositions generally at low addition levels. Therefore, it is particularly required that such compounds be distributed uniformly in said compositions. In particular, the levels of addition of folic acid and vitamin B.sub.2 are low in most instances. However, since they occur as fine crystalline powders having a high specific volume and showing a strong tendency toward aggregation, their flowability and handling properties are poor and unsatisfactory. Therefore, for preparing homogeneous compositions, a preliminary dilution step is generally employed in which they are diluted 10-, 100- or 1,000-fold, for instance, with starch, alpha-starch, lactose or some other appropriate excipient.
A method of obtaining free-flowing powders that has already been provided comprises contacting a composition which is spray dried with ultra-fine particle sized absorbents and effecting spray drying (Japanese Patent Application KOKAI No. 49-7415). However, the ultra-fine absorbent to be used is an inorganic material unsuited for pharmaceutical purposes. In addition, the method fails to give compositions containing folic acid or vitamin B.sub.2 in high concentrations.
Another method that has been provided for preparing a vitamin B.sub.2 composition capable of being directly submitted to tableting (Japanese Patent Application KOKAI No. 62-174013) gives granules on fluidized bed granulation using a macromolecular compound, such as water-soluble cellulose, as a binding agent. However, this method can hardly be applied to the manufacture of pharmaceutical preparations which should contain vitamin B.sub.2 in very low concentrations, for instance.
In some of the prior art compositions, the proportion of the excipient is too high for incorporation of other active ingredients into the compositions, while in others the excipient itself is unsuited for pharmaceutical preparations. These are the problems that remain to be solved.
Accordingly, the advent of a composition which contains a vitamin B group compound, such as folic acid or vitamin B.sub.2, has a low excipient content, has good flowability but no tendency toward aggregation, and can be used in the manufacture of pharmaceutical preparations is desired.